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The intramolecular and long-range ferromagnetic coupling between p-phenylenediamine radical cations in head-to-tail coupled oligo(1, 4-phenyleneethynylene)s and oligo(1,4-phenylenvinylene)s between neighbors and next-nearest neighbors is described. UV/vis/near-IR experiments show that the radical cations are localized in the pendant p-phenylenediamine units of the conjugated oligomers. The ESR spectra of these oligo(1,4-phenyleneethynylene) and oligo(1, 4-phenylenvinylene) di(radical cation)s are consistent with those of a triplet state. A linear behavior is observed for the doubly integrated ESR intensity of the DeltaM(s) = +/-1 and DeltaM(s) = +/-2 signals with the inverse temperature (I approximately 1/T), consistent with Curie's law. This behavior indicates a triplet ground-state diradical with a large triplet-singlet energy gap or possibly a degeneracy of singlet and triplet states. 相似文献
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Martinez-Diaz MV Rodriguez-Morgade MS Feiters MC van Kan PJ Nolte RJ Stoddart JF Torres T 《Organic letters》2000,2(8):1057-1060
[formula: see text] New unsymmetrically substituted DB24C8-phthalocyanines, which are able to form complexes with suitable dialkylammonium cations, have been prepared. These complexes most probably have a pseudorotaxane geometry. 相似文献
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Lantz MA Hug HJ van Schendel PJ Hoffmann R Martin S Baratoff A Abdurixit A Guntherodt H Gerber C 《Physical review letters》2000,84(12):2642-2645
A low temperature scanning force microscope (SFM) operating in a dynamic mode in ultrahigh vacuum was used to study the Si(111)- (7x7) surface at 7.2 K. Not only the twelve adatoms but also the six rest atoms of the unit cell are clearly resolved for the first time with SFM. In addition, the first measurements of the short range chemical bonding forces above specific atomic sites are presented. The data are in good agreement with first principles computations and indicate that the nearest atoms in the tip and sample relax significantly when the tip is within a few A of the surface. 相似文献
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The volatile constituents of Valeriana jatamansi Jones and V. hardwickii Wall. (Valerianaceae) collected from the Khasi Hills of north-east India were analyzed by GC and GC/MS. Twenty-seven and twenty-one compounds were characterized and identified from V. jatamansi and V. hardwickii samples, representing 90.6% and 82.7% of the total oil, respectively. Sesquiterpenes were shown to be the main constituents in both the oil samples. Maaliol (26.1%), patchouli alcohol (9.3%) and a-gurjunene (8.7%) were the major components of V. jatamansi oil, whereas valeracetate (21.3%), methyl linoleate (14.1%), bornyl acetate (13.8%) and cuparene (7.1%) were the main constituents of V. hardwickii oil. Both Indian valerian essential oils were studied for their antioxidant activities using the free radical-scavanging activity (DPPH) and ferric reducing antioxidant power (FRAP) assays. V. hardwickii oil exhibited a higher antioxidant capacity than V. jatamansi in both assays. For both the valerian oil samples, there was a concentration-dependent increase in free radical scavenging activity and ferric reducing capacity. Both valerian oils and their ingredients are potential sources of natural antioxidants. 相似文献